Outrigger style building constructions are well known and commonly used in the construction of tall buildings. Outrigger systems operate by creating a functional link between two structural systems, namely the internal core system and a perimeter system, such as external gravity columns. This arrangement is illustrated schematically in FIG. 1A. A building core 10 forms the internal support structure of a building, with perimeter columns 20 forming the external support structure of the building. The core 10 and perimeter columns 20 are physically connected by a stiff outrigger beam 30. While only a single outrigger beam 30 is illustrated, there could be a plurality of these up the height of the structure, depending on the height of the building. Combining these two systems leads to a positive interaction between the combined systems, particularly in resisting lateral loads applied to the building structure. The outrigger beams 30 are used to substantially increase the stiffness of the lateral load resisting system. When the building is subjected to lateral wind or earthquake loads the internal core wants to bend as a cantilever, but is resisted by the stiff outrigger beam which engages the external gravity columns vertically, as shown in FIG. 1B. In this configuration, significant care must be taken to ensure the structural members can resist the large forces introduced in the outrigger beam under lateral loads, as well as differential vertical movement between the columns and structural core due to different long-term settlement of the gravity columns and internal building core, particularly in reinforced concrete structural systems. These effects are widely known in the art.
U.S. Pat. No. 7,987,639 describes a damping system which has been adapted for use with an outrigger configuration, as illustrated in FIG. 2A. In this application, a stiff horizontal outrigger member 70 is connected to the building core 50 on one end and to a damper 40 on the other end. The damper 40 in turn connects the outrigger member 70 to the external perimeter columns 60. The damper as described in the aforementioned patent consists of a viscoelastic material bonded between interdigitated structural steel plates which are then anchored directly into the horizontal outrigger beam as well as the external gravity columns. When a building is deformed due to lateral wind or earthquake vibrations, large relative vertical displacements are introduced in-between the steel plates deforming the viscoelastic material in shear, as shown in more detail in FIGS. 2B and 2C. This shearing of the viscoelastic material adds damping to the coupled core-outrigger-perimeter building structure.
One problem of this prior art approach to damping in an outrigger arrangement is the differential vertical movement between the perimeter columns and the structural core due to different long-term relative movement of the perimeter columns and the internal building core. This movement and settling of the building can lead to complex design requirements, and the viscoelastic material layers in the damper run the risk of tearing or not operating as originally designed once the core and perimeter columns have moved relative to one another without adjusting the connection to compensate for the movement. That is, the relative position of the core with respect to the perimeter columns may differ slightly from the position when the building is constructed and parameters under which the damper is designed.
One other example of damping in an outrigger structure is shown in PCT publication number WO2007045900 to Ove Amp and Partners International Limited, however this system also fails to sufficiently remedy at least some of the problems mentioned above, and also has the problem of requiring regular or semi-regular maintenance to the dampers in this system. In addition, this prior art system does not exhibit a viscoelastic response which allows for coupling and damping and does not exhibit effective damping over the entire wide range of displacements that is expected for wind and earthquake loading.
Accordingly, there is a need in the art for providing improved damping in outrigger building configurations.